Data Storage devices such as disc drives are commonly used in workstations, personal computers, laptops and other computer systems to store large amounts of data in a form that can be made readily available to a user. In addition, disc drives are also making their way into a wide variety of consumer electronic devices such as MP3 players. In general, a disc drive comprises a magnetic disc that is rotated by a spindle motor. The surface of the disc is divided into a series of data tracks. The data tracks are spaced radially from one another across a band having an inner diameter and an outer diameter.
Each of the data tracks extends generally circumferentially around the disc and can store data in the form of magnetic transitions within the radial extent of the track on the disc surface. An interactive element, such as a magnetic transducer, is used to sense the magnetic transitions to read data, or to transmit an electric signal that causes a magnetic transition on the disc surface, to write data. The magnetic transducer is mounted by a head structure to a rotary actuator arm and is selectively positioned by the actuator arm over a preselected data track of the disc to either read data from or write data to the preselected data track of the disc, as the disc rotates below the transducer. The actuator arm is, in turn, mounted to a voice coil motor that can be controlled to move the actuator arm across the disc surface.
A servo control system is typically used to control the position of the actuator arm to insure that the head is properly centered over the magnetic transitions during either a read or write operation. In a known servo control system, servo position information is recorded on the disc surface between written data blocks, and periodically read by the head for use in a closed loop control of the voice coil motor to position the actuator arm. Such a servo arrangement is referred to as an embedded servo system and the recorded servo position information is referred to as a servo pattern. The servo pattern is typically written on the data tracks in discrete spokes radiating out from the center of the disc.
The data tracks of a disc in the disc drive cannot be allowed to interfere with one another. If interference occurs, i.e. the read/write heads move off-track, the data previously written to a track will be overwritten and the data will be corrupted. In order to avoid interference of the data tracks, the servo control system discussed above is utilized to maintain the position of the read/write heads over the center of the data track.
Under normal operating conditions, the servo control system performs well using the feedback provided by the servo pattern to predict the read/write head location at the next area of the servo pattern and to reject disturbances which the disc drive is subjected to. However, when the disc drive experiences a very large mechanical shock, the rate of change of position and/or velocity of the read/write head position exceeds the servo system's capability to predict the head location at the next area of the servo pattern. The disc drive uses the predicted position to terminate any write operations it is performing before any adjacent track data corruption occurs. When the large shock occurs, and the head movement exceeds the servo prediction capability, and write corruption can occur.
The present invention provides a solution to this and other problems, and offers other advantages over previous solutions.